Amyotrophic lateral sclerosis (ALS) is a devastating neurological disease characterized by the selective degeneration of motor neurons in adults. Most ALS patients develop limb weakness initially, which progresses quickly to generalized muscle atrophy and paralysis. Death occurs within 5 years, usually due to respiratory failure. Despite improved understanding of ALS pathogenesis, there are still no effective treatments. Considerable hope attaches to stem cell therapy, but many obstacles must be overcome before treatment with human neural stem cells (hNSCs) becomes reality. As to mechanisms, increases in oxidative stress and excitotoxicity are known to play critical roles in disease progression. Further, oxidative stress and excitotoxicity create a harsh environment in the ALS spinal cord, which is presumably a major problem for stem cell grafting. Our hypothesis is that the toxic environment of the ALS spinal cord contributes to the death and degeneration of both grafted hNSCs and endogenous motor neurons and that the administration of the anti-oxidant, a-lipoic acid, in combination with hNSCs will increase survival of both the grafted cells and endogenous motor neurons, delaying disease progression and prolonging survival in the transgenic ALS rat model. Specific Aim 1 is to determine whether ALS astrocytes and microglia adversely effect hNSCs through oxidative damage. This will be tested using an in vitro co-culture system in which astrocytes and microglia isolated from the spinal cords of young (1 mo.) and old (5 mo.) transgenic ALS rats as well as wildtype (control) rats will be cultured with primed and differentiated hNSCs. Cell differentiation, apoptosis and markers of oxidative stress in the hNSCs will be characterized with and without a-lipoic acid addition. Specific aim 2 is to determine whether the intrathecal infusion of a-lipoic acid in combination with hNSC grafting will increase grafted cell survival and will act synergistically with hNSC grafting to delay disease progression and prolong survival in the transgenic ALS rats. In addition to measurements of bodyweight, motor function, diaphragm muscle function through electromyography and lifespan, rat spinal cords will be subjected to morphological analyses of grafted cell fate and stereological analysis of grafted cell survival. The ultimate goal of this project is to develop a combination of stem cell and anti-oxidative therapy for amyotrophic lateral sclerosis (ALS). Particularly, the morphological and functional outcomes of human neural stem cell grafting and anti-oxidant treatment in the ALS rat model will be examined.